The present invention relates to a display device, and in particular, relates to a liquid crystal display device that hardly causes light leakage at an area around a screen, and has a terminal portion with improved reliability.
The liquid crystal display device includes a TFT substrate having pixels with pixel electrodes and thin film transistors (TFT) arranged in a matrix, and a counter substrate that faces the TFT substrate and has color filters at the positions corresponding to the pixel electrodes of the TFT substrate, while interposing a liquid crystal between the TFT substrate and the counter substrate. An image is generated by controlling transmittance of light through liquid crystal molecules for each pixel.
The liquid crystal display device with a flat light-weighted structure has been widely used in various fields. Mobile phones and DSCs (Digital Still Camera) have employed compact liquid crystal display devices. The liquid crystal display panel is configured to bond the TFT substrate and the counter substrate by a sealing material applied to the peripheral area. An ultraviolet curing resin may be employed as the sealing material. However, since the light shielding film is applied to the peripheral area for higher contrast, the ultraviolet ray is unlikely to reach the sealing material. JP-A-2007-140561 discloses the structure that the light shielding film is formed on the TFT substrate and the counter substrate alternately, and is irradiated with the ultraviolet ray from both sides of the TFT substrate and the counter substrate so that the sealing material is cured. The light shielding film that is alternately formed on the side of the TFT substrate and the counter substrate of the aforementioned structure ensures shielding against light emitted from the backlight.
Formation of the black matrix extending to the end part of the counter substrate is effective for prevention of light leakage from the backlight around the liquid crystal display panel. If the black matrix is formed to extend to the end part of the counter substrate, it is difficult to visually confirm an alignment mark from the counter substrate, which is referred to align the TFT substrate with the counter substrate. JP-A-2011-170134 discloses the structure that the frame-like part with no black matrix is provided, from which visual confirmation of the alignment mark is allowed.
The liquid crystal display panel has an injection hole formed by opening a part of the sealing material formed around the panel, through which the liquid crystal is injected so as to bond the TFT substrate and the counter substrate. JP-A-2008-257014 discloses the structure that the alignment mark is formed around the injection hole for preventing the light leakage from the injection hole so as to ensure both light shielding effect and work for alignment of the TFT substrate with the counter substrate.
FIG. 6 is a cross sectional view showing a mechanism of the generally employed liquid crystal display device, having the light leakage from the backlight around the peripheral area of the screen to deteriorate contrast around the screen. Referring to FIG. 6, a TFT substrate 100 and a counter substrate 200 are bonded by a sealing material 50, while having an inner space defined by those substrates filled with a liquid crystal 300. A black matrix 202 is formed on the counter substrate 200, but is not extended to an end part of the counter substrate 200 so as to prevent such problem as peel-off of the black matrix 202. The light from the backlight is partially emitted from peripheral areas of the TFT substrate 100 and the counter substrate 200 toward the screen while repeating total reflection on the TFT substrate 100.
The liquid crystal display panel is stored in a frame 400 with a flange 401. The light ray incident on the counter substrate 200 at a certain angle is emitted toward the screen to deteriorate the contrast. In order to prevent such deterioration, it is preferable to form the black matrix 202 to extend to the end part of the counter substrate 200. However, the liquid crystal display panel is obtained by dividing a mother substrate into a large number of liquid crystal display panels through scribing. The end part of the liquid crystal display panel is exposed to mechanical stress. As a result, the black matrix 202 formed to extend to the end part may cause a risk that is likely to cause the peel-off of the black matrix 202 at the end part of the counter substrate 200.
If the black matrix 202 is peeled off at the end part of the counter substrate 200, water may infiltrate the end part, and intrude to the inside of a sealed portion of the liquid crystal display panel along the boundary surface between the black matrix 202 and the counter substrate 200, deteriorating reliability of the liquid crystal display device.
In order to prevent the deterioration, the black matrix 202 is not formed to extend to the end part of the counter substrate 200. Instead, a light shielding metal 20 is formed on the TFT substrate 100 to extend to the end part thereof, resulting in the model that exhibits the light shielding effect with respect to the backlight around the liquid crystal display panel. FIG. 7 illustrates a mother substrate 500 that includes four liquid crystal display panels each configured as described above. Actually, the mother substrate 500 includes far more liquid crystal display panels than four. FIG. 7 shows only four liquid crystal display panels for clear understanding.
Referring to FIG. 7, the mother substrate 500 is divided into the respective liquid crystal display panels along cutting-plane lines 40. The black matrix 202 is formed on an area around a display region 10 of the counter substrate of each liquid crystal display panel to reach the area adjacent to the end part. The light shielding metal 20 is formed on the TFT substrate to extend to the end part thereof. In other words, the light shielding metal 20 is separated along the cutting-plane lines 40.
The cutting-plane line 40 may vary with a predetermined tolerance for separation of the liquid crystal display panels from the mother substrate 500. For this, the light shielding metal 20 is formed to run over the area of the liquid crystal display panel C so as to make sure that the light shielding metal 20 is formed to extend to the end part of the liquid crystal display panel D.
FIG. 8 is a plan view illustrating that a part of the light shielding metal 20 of the liquid crystal display panel D remains at the end part of a terminal portion of the liquid crystal display panel C after its separation from the liquid crystal display panel D. Referring to FIG. 8, the TFT substrate 100 is formed to be larger than the counter substrate 200. An extended part of the TFT substrate 100 serves as a terminal portion 150 to which a not shown flexible wiring substrate is connected. As FIG. 8 shows, the black matrix 202 is formed to extend to the peripheral area of the counter substrate 200, and the light shielding metal 20 is formed to extend to the end part of the TFT substrate 100 except the terminal portion 150.
The shielding metal 20 linearly formed on the liquid crystal display panel D as shown in FIG. 7 remains at the outer end part of the terminal portion 150 shown in FIG. 8. The light shielding metal 20 may cause the risk of short circuit in a wiring on the flexible wiring substrate upon its connection to the terminal portion 150 as described below.
FIG. 9 is a sectional view taken along line A-A of FIG. 8. Referring to FIG. 9, the TFT substrate 100 and the counter substrate 200 are bonded by a sealing material 50. A liquid crystal 300 is sealed inside the sealing material 50. The black matrix 202 is formed on the inner side surface of the counter substrate 200, which exceeds from the sealing material 50 to the area around the end part. The light shielding metal 20 is formed at the side of the TFT substrate 100 to its end part under an inorganic passivation film 106. This makes it possible to prevent leakage of light rays from the backlight at the end part of the liquid crystal display panel.
FIG. 10 is a sectional view taken along line B-B of FIG. 8. Referring to FIG. 10, the TFT substrate 100 and the counter substrate 200 are bonded by the sealing material 50. The black matrix 202 is formed on the inner side surface of the counter substrate 200 to the area around the end part. The TFT substrate 100 is formed to be larger than the counter substrate 200. The extended part of the TFT substrate 100 serves as the terminal portion 150, an end part of which is connected to the not-shown flexible wiring substrate.
Referring to FIG. 10, the light shielding metal 20 of the adjacent liquid crystal display panel of the mother substrate remains at the end part of the terminal portion 150. In this way, the remaining light shielding metal 20 may cause the risk of short-circuit in the wiring on the flexible wiring substrate upon its connection.
FIG. 11 is a perspective view of a part around the terminal portion 150 of the liquid crystal display panel for explanation about the aforementioned problem. Referring to FIG. 11, a flexible wiring substrate 30 is connected to the terminal portion 150 of the TFT substrate 100. A wiring 31 is formed on the flexible wiring substrate 30. The wiring 31 is mostly coated with an insulating resin while the wiring 31 around the terminal of the flexible wiring substrate 30 is in a bare state.
This may cause the risk of short-circuit in the wirings 31 on the flexible wiring substrate 30 owing to the light shielding metal 20 that remains at the end part of the TFT substrate 100. Since the flexible wiring substrate exhibits flexibility, there may be the case where the light shielding metal 20 is brought into contact with the wiring 31 on the flexible wiring substrate 30 at points of C and D shown in FIG. 11, for example, resulting from bending of the substrate at the position near the terminal portion 150. This may cause short-circuit in the wirings 31.